Nutrition is a key determinant of long-term health, and social influence has long been theorized to be a key determinant of nutrition. It has been difficult to quantify the postulated role of social influence on nutrition using traditional methods such as surveys, due to the typically small scale and short duration of studies. To overcome these limitations, we leverage a novel source of data: logs of 38 million food purchases made over an 8-year period on the Ecole Polytechnique Federale de Lausanne (EPFL) university campus, linked to anonymized individuals via the smartcards used to make on-campus purchases. In a longitudinal observational study, we ask: How is a person's food choice affected by eating with someone else whose own food choice is healthy vs. unhealthy? To estimate causal effects from the passively observed log data, we control confounds in a matched quasi-experimental design: we identify focal users who at first do not have any regular eating partners but then start eating with a fixed partner regularly, and we match focal users into comparison pairs such that paired users are nearly identical with respect to covariates measured before acquiring the partner, where the two focal users' new eating partners diverge in the healthiness of their respective food choice. A difference-in-differences analysis of the paired data yields clear evidence of social influence: focal users acquiring a healthy-eating partner change their habits significantly more toward healthy foods than focal users acquiring an unhealthy-eating partner. We further identify foods whose purchase frequency is impacted significantly by the eating partner's healthiness of food choice. Beyond the main results, the work demonstrates the utility of passively sensed food purchase logs for deriving insights, with the potential of informing the design of public health interventions and food offerings.

中文翻译：

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社会纽带的形成影响食物选择：一项校园范围的纵向研究

营养是长期健康的关键决定因素，长期以来，人们一直认为社会影响是营养的关键决定因素。由于研究规模通常较小且持续时间较短，因此难以使用传统方法（如调查）来量化社会影响对营养的假定作用。为了克服这些限制，我们利用了新颖的数据源：在8年的时间内，在洛桑联邦理工大学（EPFL）大学校园内购买了3,800万份食品，并通过用来制作智能手机的匿名卡链接到匿名个人。 -校园购买。在一项纵向观察性研究中，我们问：与自己饮食选择健康与不健康的其他人一起吃饭会影响一个人的饮食选择吗？要根据被动观察到的日志数据估算因果关系，我们以匹配的准实验设计控制混杂因素：我们识别最初没有任何常规饮食伙伴但随后开始与固定伴侣开始饮食的重点用户，然后将重点用户分成比较对，以使配对用户几乎相同关于在获取合作伙伴之前测得的协变量，这两个主要使用者的新饮食合作伙伴在各自食物选择的健康性方面存在差异。对配对数据进行的差异分析清楚地表明了社会影响力：与获取不健康饮食伙伴的重点用户相比，获得健康饮食伙伴的重点用户将其习惯向健康食品的改变明显更大。我们进一步确定那些购买频率受饮食伙伴的食物选择健康程度显着影响的食物。